In July, three months after construction began on the foundation of the 92-story Trump International Tower and Hotel, water began leaking into the building site from the Chicago River.

With the foundation being laid next to and below the level of the river, it always was a possibility that the old sea wall wouldn't hold. It did, but water began seeping through seams in a corner where the wall meets the Wabash Avenue bridge.

The construction of any building is not just the grand achievement of architects and engineers. It is the culmination of a million tiny tasks, and the triumph of overcoming a million tiny problems--any of which could become a crisis.

The difficulties in building the biggest building in a generation in Chicago go beyond just bricks and mortar. They started with the job of finding the site, creating the design and raising the money. They continue with putting the building up and keeping costs down.

In fact, there are bigger issues than seeping water or worries about dropping a 140-foot beam on the roof of the IBM building's garage next door. One is preventing the project from buckling under the rising costs of construction materials.

"What I really worry about is all the trades I haven't bought," said Paul James, using construction industry jargon for the millions of dollars of materials he has yet to purchase for the interior of the building. James is overseeing the project for the construction manager Bovis Lend Lease Inc. of London.

From the outside, none of this is visible. Passersby who peer down into the construction site from a temporary pedestrian walkway see a modest-size pit along the Chicago River.

"But it's much more," said Donald Trump Jr., vice president of development and acquisition for the company whose chief executive is his flamboyant father.

Since last fall, Trump Corp. has demolished the Chicago Sun-Times building that stood on the 2-acre site and completed some of the project's most difficult spadework, which is key to the structural integrity of the 2.7 million-square-foot tower.

The ear-shattering percussion of pounding 241 supports, called caissons, deep into the earth may have jangled neighbors' nerves. But to the New York-based developer it is essential to laying the foundation for the approximately $800 million building.

It had to drive 57 of the caissons 110 feet into limestone bedrock, a feat reserved for construction of the tallest towers here.

"The Trump edge is understanding construction," Trump, 27, said on one of his weekly visits to the site.

The rest of the foundation system and basements are being built on the caissons, which will support the weight of the entire tower, equivalent to 240,000 cars.

In October, workers will pour the high-strength concrete for the steel-reinforced mat that will unite and secure the caissons. Upon the mat--which will be 240 feet long, 60 feet wide and 10 feet deep--will rest the tower's core walls.

By next year, the core walls will start to rise. By fall 2007, portions of the building are expected to be ready for occupancy. The tower, which will house 758 private and hotel condominiums as well as retail space, is expected to be finished in 2009, Trump Jr. said.

In part, the Trump construction formula is about selective cost-cutting, which Trump Jr. said he learned at his father's elbow, following him around building sites just as his father trailed after his grandfather.

To keep costs down, he said, "We don't let architects build every feature." But it's also about simplifying the process.

So far, the construction work completed is worth near $30 million, or 5 percent of Trump's $600 million construction budget. Another $200 million will be spent on other aspects of the development. But no matter how smoothly construction goes, erecting a 1,362-foot-tall tower is a complex undertaking.

"Tall buildings are more demanding as an engineering solution," said architect Richard Tomlinson, a partner at Skidmore, Owings & Merrill, LLP. His firm designed the Trump project as well as the Sears and Hancock towers in Chicago.

The Trump tower will stack retail, parking, a hotel and condominiums on top of each other. This change of uses changes the design of the interior space.

A three-bedroom residential condominium will have bathrooms in different locations than a hotel suite. Therefore, plumbing can't descend directly down the tower but must at times be routed horizontally, which makes the system more costly and its operation more difficult to fine tune.

The same is true of load-bearing columns. The 14 million pounds that each column carries must be transferred horizontally via huge girders. "As the tallest tower to be built post-9/11, it's a celebrated project," said John Fish, chief executive of Boston-based Suffolk Construction Co., a major East Coast builder who is watching the project's progress. "But it poses special construction challenges."

With the price of construction materials up sharply in the last two years, cost containment on such a mammoth project is a chore, Fish said.

For instance, the average nationwide price of concrete, the material being used for the foundation and frame, increased 14.5 percent during the last year, according to Engineering News Record, a trade publication. Last fall, after an 18-month debate, Trump decided on an all-concrete frame, in part to eliminate the expense of using structural steel, a commodity whose price had doubled since summer 2003.

Still, James is concerned about materials required to build out the interior because they have not yet been purchased, and prices could rise as a result of rebuilding efforts in the nation's storm-damaged areas.

Further, such a large project requires so much construction material that it can pinch supplies, raising prices throughout the marketplace, said Ron Klemencic, chairman of the Council on Tall Buildings and Urban Habitat.

In April, Trump Corp. started to build the foundation system below the Chicago River; in August, contractors started to excavate for the basements.

"This is probably the trickiest part of the construction process," said Stephen Fort, general manager of the Chicago office for Turner Construction Co., which is not involved in the project but, like most in the industry, is watching with interest.

"When you're in the hole, there are so many unknowns, you don't control your own destiny," he said.

In the spring, Trump Corp. sealed an old freight tunnel and removed dock pilings from the site. But in July water started seeping in and the builders had a problem. They sent divers into the murky river to see whether the leak could be sealed from the water side. That failed, as did several other attempts to correct the problem. Finally, they came upon a solution.

"We drove a steel plate next to the gap, dug out the space between and filled it with concrete," James said. "That worked. In a big project like this there are lots of opportunities to have major things go wrong. This wasn't one of them."

Most of the tower's caissons descend into hard clay about 75 feet down, but others were drilled an extra 35 feet, including 6 feet into bedrock.

"That's a long way, made tougher by managing the water in the hole," Klemencic said.

Meanwhile, a concrete pump for the project is being custom-made in Germany. Every hour its 630-horsepower engine will be able to pump 100 cubic yards of concrete and send it as high as 1,700 feet.

Still, the old Sun-Times building that Trump purchased for $74 million, including the land, has proven to be an unexpected boon, Trump Jr. said.

During site preparation last fall, the company encountered less ground pollution from the printing plant than anticipated because in the 1970s the newspaper switched from petroleum-based to soy-based ink. Trump therefore avoided some costly site cleanup.

Finally, the company saved at least $1 million by reusing the Sun-Times' old sea wall.

"In the 1950s, the Sun-Times built it to withstand another sort of terrorism: the Cold War," Trump Jr. said. "It was as thick as a bomb shelter."

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Trump's tower

HEIGHT: 92 stories, or 1,362 feet, the tallest skyscraper to go up in the U.S. since the 1992 completion of the Bank of America Plaza in Atlanta.

ARCHITECT: Skidmore, Owings & Merrill LLP, which designed the Sears Tower, at 1,450 feet, the nation's tallest building, and the John Hancock building, at 1,127 feet.

A burst of thunderstorm activity across the Chicago area in Sunday afternoon resulted in multiple injuries and a death at an event in west suburban Wood Dale, the collapse of a dome in northwest suburban Rosemont and the temporary evacuation of the music festival Lollapalooza in Grant Park downtown.

Now there are two: Zimbabwe accused a Pennsylvania doctor on Sunday of illegally killing a lion in April, adding to the outcry over a Minnesota dentist the African government wants to extradite for killing a well-known lion named Cecil in early July.